The present invention relates to selected 2-aryl-2H-benzotriazoles which are useful in protecting light-sensitive organic materials from deterioration and to stabilized compositions containing said benzotriazoles.
The UV absorbers of the o-hydroxyphenyl-2H-benzotriazole class have long been known as effective light stabilizers for organic materials and have enjoyed considerable commercial success.
However, the hitherto known 2-aryl-2H-benzotriazoles of this group have in some circumstances exhibited limited compatibility in certain substrates, and excessive tendency to exude, sublime and/or volatilize during processing of stabilized compositions into sheets, films, fibers or other pellicles when processing must be done at elevated temperatures. Likewise such benzotriazoles may also suffer undue loss by volatilization or sublimation from fabricated structures, particularly thin films or coatings, especially when subjected to elevated temperatures during use.
Attempts have been made to increase substrate compatibility or solubility and to reduce volatilization loss by modifying the structure of the benzotriazoles.
In U.S. Pat. No. 3,230,194, a higher alkyl group was substituted for methyl and the compound 2-(2-hydroxy-5-tert-octylphenyl)-2H-benzotriazole exhibited superior compatibility and performance in polyethylene.
In U.S. Pat. No. 4,127,586, still other modifications to the 2-aryl-2H-benzotriazole moiety were made to increase still further compatibility in substrates and resistance to volatilization. The compound 2-[2-hydroxy-3-(1-phenylethyl)-5-methylphenyl]-2H-benzotriazole described therein exhibited better compatibility and better resistance to loss by volatilization during processing than did the earlier prior art benzotriazole compounds.
In Japanese Kokai No. 158588/75, other benzotriazole light stabilizers such as 2-(2-hydroxy-3-alpha, alphadimethylbenzyl-5-methylphenyl)-2H-benzotriazole are disclosed.
However, still better resistance to loss from stabilized compositions during high temperature processing remained a practical objective and need in the art for the benzotriazole UV-absorbers.
U.S. Pat. No. 4,226,763 describes attempts to increase the resistance of benzotriazole light absorbers to loss by volatilization. This patent describes 2-(2-hydroxy-3,5-di-alpha-cumylphenyl)-2H-benzotriazole which exhibits superior resistance to loss from stabilized compositions during high temperature processing or in end use applications where coatings or films of the stabilized compositions are exposed even to ambient weathering and light exposures compared to stabilized compositions containing the 2-aryl-2H-benzotriazoles of the prior art. This superior performance is attained at the cost of relatively low solubility in some substrates and processing solvents.
U.S. Pat. No. 4,283,327 describes 2-(2-hydroxy-3,5-di-tert-octylphenyl)-2H-benzotriazole which exhibits enhanced solubility in processing solvents and substrates, but which did not have outstanding resistance to loss by volatilization.
U.S. Pat. No. 4,278,589 describes benzotriazoles having one alpha-cumyl group and one tert-octyl substituent on the 2-phenyl moiety in an attempt to achieve a balance of properties not obtained with two alpha-cumyl or with two tert-octyl groups. Benzotriazoles with a good balance of solubility and resistance to loss by volatilization were obtained, but not the outstanding levels of each required by an increasingly demanding market place for light stabilizers with truly exceptional properties.
Although lower alkyl, and halogen substitution on the benzo ring of 2H-benzotriazoles has long been known for example in U.S. Pat. No. 4,127,586 and Japanese Sho 59/172,655, the substitution of the benzo ring with higher alkyl, groups is not known.
Traditionally lacquers have been used in the automotive and other industries to produce high gloss coatings. Such lacquers typically consist of high molecular weight polymers dissolved in appropriate solvents. The solvents which usually constitute over 70% of the paint evaporate on baking to leave a polymer film.
Energy and environmental considerations have more recently resulted in development of so called "high solids enamels" as alternate coating systems, which meet government mandated reduction in "volatile organic compounds (VOC)". High solids enamels typically consist of low molecular weight copolymers of methyl methacrylate, hydroxyethyl methacrylate, butyl acrylate and styrene. Such copolymers which contain pendant hydroxyl groups are then blended with melamine crosslinking resins (ratios of about 7:3). The final crosslinking reaction occurs when the painted article is subjected to baking. High solids enamels in contrast to lacquers contain usually less than 50% solvent.
The bulk of these solvents are employed during the monomer polymerization process. Only a small quantity of solvents generally less than 10% of the total solvent is retained as "hold out" solvent to be added later to the final paint. The light stabilizing additives must be soluble enough in this hold out solvent to permit incorporation at this stage. The amount of solvent cannot be changed at will because paint viscosity is a critical parameter in avoiding defect such as runs and sags. To meet these demands for high solubility the instant stabilizers were developed. These products also meet and/or exceed that state of the art materials with respect to compability with the resin and lack of volatility.